Encapsulated electroluminescent lamps have been commercially available from many vendors for many years. Although such lamps are sometimes structurally rigid in design, more commonly they are made in flexible form. Such encapsulated electroluminescent light sources are often used for instrument panels and are particularly uniquely attractive for use as exterior lighting for aircraft or other vehicles. Thus, an electroluminescent lamp which provides an area light source on the fuselage or wings of an aircraft can be used to judge distance and orientation, in contrast with a point light source, i.e., a filament lamp, which provides relatively poor depth perception and judgment of distance. Further, although filament lamps may show excellent lifetimes under laboratory conditions, they are particularly susceptible to vibration failure, while electroluminescent lamps do not share such vulnerability. Further, filament lamps require space within the structure of an aircraft for the lamp assembly, with only the lens flush with the skin. On the other hand, electroluminescent lamps, due to their unique geometry, can replace structural panels or form an overlay bonded to the skin of an aircraft, for example. It is found that filament lamps installations have a mean time to failure which is inversely proportional to the number thereof which are used in a particular installation. Thus, as the number of filament lamps rises, the probability of a failure increases, thereby creating an owner risk maintenance problem. While filament lamps fail catastrophically (i.e. complete failure substantially at one instant of time), electroluminescent lamps, if correctly constructed, do not fail catastrophically but exhibit brightness decay characteristics independent of the lighted area being provided. The decay of modern lamps is sufficiently low to be particularly acceptable for the applications discussed above.
There has been an increasing need for electroluminescent lighting assemblies for use in high performance aircraft where the environmental and temperature requirements for the lamps are very severe. Such lamp assemblies must have the ability to repeatedly withstand exposure to temperatures as high as 360.degree. F at an ambient pressure corresponding to an altitude of 80,000 feet. Further, they must be able to withstand continuous exposure to tropical sunlight, to salt spray, to vibration, to thermal shock, and to high humidity conditions. Combinations of such conditions tend to render inoperative and to structurally damage electroluminescent lamps and assemblies which are presently available, and it is desirable that lamp assemblies be designed to survive these conditions without damage and subsequently to meet all operational requirements at reasonable cost.